I’ve found some time to look at the OpenSprinkler firmware in more detail.
Opensprinkler firmware 2.1.9(7) periodically polls the weather service every 6 hours. The corresponding code can be found on GitHub in OpenSprinkler/OpneSprinkler-Firmware /main.cpp, line 59:
#define CHECK_WEATHER_TIMEOUT 21613L // Weather check interval (in seconds)
Looking up older firmware releases shows that the weather service check interval was increased from 1 hour to 2 hours with firmware release 2.19(4) and thereafter from 2 to 6 hours with firmware release 2.19(5).
Reason for this increased weather check interval is to reduce jamming the weather service as this will produce additional costs in regards to using costly weather providers. However, there are some problems if the sprinkler activity is planned to start at sunrise time or earlier than 6am in the morning:
• Common weather changes, like early morning rainfalls remain probably be unrecognized by OpenSprinkler and lead to wasted water.
• In regards to using weather adjustment methods like Zimmerman, the calculated water level polled by OpenSprinkler may be outdated or not based on yesterday’s
To avoid these problems I used a programmable power timer to restart OpenSprinkler every Sunday at 0:45am. This leads to a weather service update for the whole week at about 6:45am in the morning well before my 7 am sprinkler watering.
Another possibility might be to shorten the service check interval to 1 hour again. This might be done by updating OpenSprinkler with a private compilation of the OpenSprinkler firmware. As already mentioned the OpenSprinkler team has to pay for all weather queries. For this reason a local weather service installation accessing a personal weather station will be mandatory to avoid any expenses for the OpenSprinkler team.
I’m currently using this updated OpenSprinkler together with a local Netatmo PWS and a Raspberry Pi weather service installation. This allows me to go back to sunrise garden watering again. However, there might be other ideas to avoid the disadvantages described above. Maybe introducing a more controlled weather service polling right before any scheduled watering program will do the job?